The present invention generally relates to an assembly for adjusting an optical element and, in particular, relates to an assembly for adjusting a compensator plate in an interferometer.
Optical beamsplitters are widely used in many applications which require two beams of light from a single source. One such use is in an interferometer. In general, an interferometer is an arrangement whereby a single beam of light is separated into two or more parts by partial reflections, the separate beams being subsequently reunited after traversing different optical paths. The reunited beams then produce interference. One practical application of an interferometer is in a Fourier Transform Infrared (FT/IR) Spectrophotometer.
As well known in the interferometer field, a path length compensation plate is usually placed in the path of the transmitted separated beam. This is required since one of the separated beams from the beamsplitter reflects back through the transparent substrate material of the beamsplitter whereas the other separated beam follows a different path. Generally, the compensator plate, in order to equalize the path length, is positioned parallel to the beamsplitter substrate and, additionally, is made to precisely the same thickness as the beamsplitter substrate.
The precision required for the thickness matching of the compensation plate and beamsplitter substrate becomes more apparent when it is recognized that each of the separated beams traverses a separate optical path two times. Hence, any errors due to mismatched pathlengths caused by thickness differences are doubled.
Meeting these positional and thickness requirements is exceedingly difficult and frequently prohibitively expensive in instruments designed for very precise measurements.